1. Field of the Invention
The present invention relates to an electronic parts substrate and a method for manufacturing the electronic parts substrate.
2. Discussion of the Background
As means of suppressing the height of an electronic parts substrate having electronic parts mounted thereon, multilayered ceramic board in each of which cavities for housing various electronic parts are provided on its top surface and bottom surface are disclosed, for example, in Japanese Patent Application Laid-Open No. 2005-354093 and Japanese Patent Application Laid-Open No. 2006-148177. Japanese Patent Application Laid-Open Nos. 2005-354093 and 2006-148177 are incorporated herein by reference in their entirety.
However, the technique disclosed in the patent documents relates to a cavity-provided multilayered ceramic board with a low thermal expansion coefficient, and its reduction in reliability originated from heat contraction hardly becomes an issue as compared with a multilayered resin board. In a case where cavities are formed in an electronic parts substrate having a lamination of insulating resins, the thermal expansion coefficient of the insulating resin is high, making the thermal stress locally greater due to the influence of the cavities. This makes the insulating resin layers and conductive circuits susceptible to cracks, causing disconnection and lowering of the reliability.